1. Field of the Invention
The present invention relates to a honeycomb metal catalyst apparatus, and more specifically to a honeycomb metal catalyst apparatus provided with a carrier body formed by spirally and alternately winding two corrugated sheet-metal layers of different wave pitches in stacked fashion.
2. Description of the Prior Art
An example of honeycomb metal catalyst apparatus used in exhaust gas systems of automotive vehicles for air pollution prevention is disclosed in U.S. Pat. No. 4,845,073 by Theodor Cyron, entitled METAL CATALYST CARRIER BODY HAVING TWO DISSIMILARLY CORRUGATED SHEET-METAL LAYERS for instance, which is incorporated herein by reference.
FIGS. 1(A) and (B) show this prior-art honeycomb metal catalyst apparatus, in which a metal honeycomb carrier body 21 is formed into a roughly cylindrical shape by spirally and alternately winding a first corrugated sheet-metal layer 23 having a relatively large wavelength (i.e. wave pitch P.sub.1) and amplitude and a second corrugated sheet-metal layer 24 having a relatively small wavelength (i.e. wave pitch P.sub.2) and amplitude in synchronized and stacked fashion so as to provide a number of conduits (honeycomb portions) 25 therebetween. In this prior-art honeycomb metal catalyst apparatus, however since the ratio of the wave pitch P.sub.1 of the first sheet-metal layer 23 and that P.sub.2 of the second sheet-metal layer 24 is determined on the basis of two integers so that the two corrugated layers are brought into contact in synchronism with each other, in the case of P.sub.2 /P.sub.1 =1/2 as shown in FIGS. 1(A) and 1(B), the troughs of the first sheet-metal layer 23 are theoretically in contact with the troughs of the second sheet-metal layer 24, so that a great number of uniform gas flow conduits 25 can be formed continuously, between the two first and second sheet-metal layers 23 and 24.
In practice, however, since it is impossible to manufacture the honeycomb metal carrier body 21 having absolutely accurate wave pitches, that is, since the wave pitches of the corrugated sheet-metal layer 23 or 24 are inevitably formed irregular to some extent, when the two corrugated sheet-metal layer 23 and 24 are expanded as shown in FIG. 1(B), there exist three regions A, B and C as follows:
In the region A, the troughs of the first layer 23 are in contact with the troughs of the second layer 24; in the region B, the troughs of the first layer 23 are slightly offset from troughs of the second layer 24; and in the region C, the troughs of the first layer 23 are in contact with the crests of the second layer 24. This is because the ratio of the wave pitch P.sub.1 of the first layer 23 and that P.sub.2 of the second layer 24 is determined on the basis of the integer relationship with respect to each other, as already described.
On the other hand, the radial (double) stack distance D between the inner troughs of the second layer 24 and the outer crests of the first layer 23 changes according to the above-mentioned three regions A, B and C. That is, the radial stack distance D.sub.1 between the two layers 23 and 24 at the region A is smaller than that D.sub.2 at the region C. Therefore, there exists a problem in that the exhaust gas flow resistance at the region C is smaller than that at the region A, so that the catalyst metal is irregularly consumed much at the region A; that is, there exists a problem in that the catalyst performance is not uniform in the honeycomb metal catalyst apparatus. In addition, since these alternately stacked or wound sheet-metal layers 23 and 24 are compressed in the radial direction and fitted into a cylindrical or an elliptically cylindrical casing, the contact pressure between the first and second layers 23 and 24 at the region A is smaller than that at the region C, so that there exists another problem in that the first and second sheet-metal layers 23 and 24 are easily separated from each other at the region A and therefore the honeycomb metal carrier body itself is deformed or damaged, thus raising various problems in reliability and service life thereof.